The present invention relates generally to turntable devices having rotary recording medium size changeover capabilities in rotary recording medium reproducing apparatuses, and more particularly to a turntable device having rotary recording medium size changeover capability in a rotary recording medium reproducing apparatus, which is capable of positively adhering rotary recording mediums of various sizes onto the upper surface of a turntable sheet in a state where the lower surface of the turntable sheet is adhered substantially throughout the entire surface with respect to a turntable, by a simple setting operation in which the turntable is rotated by a small amount.
Heretofore, in apparatuses for reproducing rotary recording mediums such as record discs, the record disc which is to be reproduced, has been merely been placed on a turntable. In such apparatuses, if the record disc is warped, the record disc will rotate in a warped state, and will not make a close contact with the turntable (a state referred to as "poor adherence"). When the record disc rotates in a warped state, the pickup arm (tone arm) is adversely caused to swing in vertical directions, following the warp of the record disc. As the pickup arm swings, the reproducing stylus in the pickup cartridge of the pickup arm is displaced in the longitudinal direction of the sound groove in the record disc. Accordingly, the reproduced signal is subjected to frequency modulation, and wow is introduced. Furthermore, the warp of the record disc causes the cantilever pickup arm to undergo rotational displacement beyond the normal range. Hence, the moving magnet or the like adapted to undergo vibratile motion in accordance with the signal recorded in the sound groove, is also displaced beyond the normal range, resulting in a loss of the linearity in the power generating efficiency. As a consequence, amplitude modulation and distortion are produced.
Moreover, if the record disc is poorly adhered to the turntable, sound from the speaker units will be fed back to the record disc in an acoustic manner, and the resulting howling phenomenon will deteriorate the quality of the reproduced sound.
Furthermore, in a rotary recording medium such as a video disc, the warp of the disc causes fluctuations in the contact state between the reproducing stylus and the rotary recording medium, thus impairing satisfactory reproduction.
Accordingly, apparatuses have been proposed for maintaining the record disc in close contact with the turntable, so as to eliminate the above described problems. In one of such apparatuses, the warp is eliminated from the record disc, and the record disc is kept in close contact with the turntable, either by placing a weight on the record disc at the center thereof or alternatively by depressing the peripheral portion of the record disc by means of a ring member. However, this apparatus gives rise to difficulties in that the warp of the record disc cannot be corrected completely, and that the manual operations involved are rather troublesome. Moreover, in another of such apparatuses, a sheet on the turntable is adapted to undergo deformation in conformance with the warp of the record disc placed thereon. The apparatus, however, has a shortcoming in that the warp of the record disc cannot be corrected, and that wow and distortion introduced cannot be eliminated.
Hence, in order to solve and eliminate the above described problems, a novel and useful turntable device having rotary recording medium size changeover capability in a rotary recording medium reproducing apparatus has been proposed in a U.S. Pat. No. 4,234,195 entitled "APPARATUSES FOR REPRODUCING SIGNALS FROM ROTARY RECORDING MEDIUMS" issued Nov. 18, 1980, in which the assignee is the same as that of the present application. According to one embodiment of a turntable device described in the above U.S. patent, the rotary recording medium is adhered onto a rotary structure such as a turntable sheet or a turntable by suction, due to the sucking action of a suction pump, to correct the warp of the rotary recording medium. According to this turntable device, the rotary recording medium can be reproduced in a warp-free state, and the placing or removing of the rotary recording medium to or from the turntable can be performed without any difficulty.
Furthermore, as another embodiment of a turntable device, the above U.S. patent disclosed a turntable device in which the area over which suction is applied at the upper surface of a rotary structure such as a turntable on which the rotary recording medium is placed, can be appropriately varied. According to this device, not only large size rotary recording mediums but also small size rotary recording medium can be drawn against the rotary structure under suction.
However, in the above turntable device in which the turntable sheet is composed of a rotary plate having a small diameter and a ring plate fitted around the periphery of the rotary plate, and suction grooves of a predetermined pattern are provided in the respective rotary plate and the ring plate, and further, the angular positions of the respective rotary plate and the ring plate are appropriately varied in order to cope with the various sizes of the rotary recording mediums which are to be adhered onto the turntable sheet by suction, there were disadvantages in that the manufacturing process and the operation of the device were troublesome and the cost of the device became high, since the turntable sheet is composed of two different sheets.
In addition, in the above turntable device in which suction grooves are respectively formed on both sides of the turntable sheet so that the allowable suction range provided by the turntable sheet corresponds to the different diameters of the rotary recording mediums, to positively adhere rotary recording medium of two different sizes by turning over the turntable sheet, there were problems in that the turntable sheet could only be used for two kinds of rotary recording mediums by performing the above operation in which the turntable sheet is turned over, and that the above operation to turn over the turntable sheet was troublesome. Moreover, when a rotary recording medium of a larger size is to be adhered onto the turntable sheet, the rotary recording medium was only adhered onto the turntable sheet under suction by the suction grooves provided for the rotary recording medium of a smaller size. Thus, the outer peripheral parts of the rotary recording medium of the larger size were not adhered with respect to the turntable sheet, and mixed oscillation modulation and the like which are introduced due to vibrations in the rotary recording medium, could not sufficiently be suppressed.
As another example of a turntable device, there is a device which copes with the different sizes of the rotary recording mediums which are to be adhered onto the turntable sheet, similar to devices used for cutting a record disc. However, the cost of this type of turntable device is exceedingly high, and cannot be applied to a normal rotary recording medium reproducing apparatus.